Feature request: Allow to customize appearance of WSTagView's

[salabaha]

currently it's not possible to change for instance corner radius of WSTagView. One way of customization is to update
open var onDidAddTag: ((WSTagsField, _ tag: WSTag) -> Void)?
func and include WSTagView as additional parameter.

[svilon]

+1. Ability to customize is essential. Would be even better to allow subclass WSTagView and provide class as default for tag.